The vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as photosynthesis, while the reproductive organs are essential in reproduction. However, if there is asexualvegetative reproduction, the vegetative organs are those that create the new generation of plants (see clonal colony).

The English word "organ" derives from the Latinorganum, meaning instrument, itself from the Greek word organon, implement, musical instrument, or organ of the body. The Greek word is related to ergon, work.[5] The viscera, when removed from a butchered animal, are known collectively as offal. Internal organs are also informally known as "guts" (which may also refer to the gastrointestinal tract), or more formally, "innards".

Aristotle used the word frequently in his philosophy, both to describe the organs of plants or animals (e.g. the roots of a tree, the heart or liver of an animal), and to describe more abstract "parts" of an interconnected whole (e.g. his philosophical works, taken as a whole, are referred to as the "organon").

The English word "organism" is a neologism coined in the 17th century, probably formed from the verb to organize. At first the word referred to an organization or social system. The meaning of a living animal or plant is first recorded in 1842.[5] Plant organs are made from tissue built up from different types of tissue. When there are three or more organs it is called an organ system[citation needed].

The adjective visceral, also splanchnic,[6] is used for anything pertaining to the internal organs. Historically, viscera of animals were examined by Roman pagan priests like the haruspices or the augurs in order to divine the future by their shape, dimensions or other factors. This practice remains an important ritual in some remote, tribal societies.

The term "visceral" is contrasted with the term "parietal", meaning "of or relating to the wall of a body part, organ or cavity".[7] The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.